1. Technical Field
The exemplary embodiments of the present invention relates to a semiconductor memory device and a method of manufacturing the same, and more particularly, to a phase-change random access memory (PCRAM) device and a method of manufacturing the same.
2. Related Art
A PCRAM device which is one of nonvolatile memory devices includes a phase-change material of which resistance is changed depending on a temperature. The phase-change material typically includes a chalcogenide material including germanium (Ge), antimony (Sb), and tellurium (Te). The phase-change material is changed into an amorphous state or a crystalline state depending on the temperature to define RESET (or logic “1”) or SET (or logic “0”).
Like a dynamic random access memory (DRAM) device, the PCRAM device may include a plurality of memory cells defined by word lines and bit lines and each of the plurality of memory cells may include a variable resistor formed of a phase-change material and a switching element configured to selectively drive the variable resistor.
In the PCRAM, the word line may be provided as a junction region type in a semiconductor substrate and a bit line may be provided as a wiring type. A diode or a MOS transistor may be used as the switching element.
The PCRAM is being researched to increase its integration degree while reducing its chip size. However, there is a limit in reducing a minimum feature size due to limitation of resolution.
For this reason, a method of manufacturing a three-dimensional (3D) PCRAM, in which a diode is formed in a vertical pillar shape or a switching transistor is formed using a vertical pillar of gate, has been suggested.
However, actually, it is difficult to form the vertical pillar in the 3D PCRAM.
In particular, to improve an off current characteristic of the diode switch element of a vertical pillar, a height of the vertical pillar is to be increased. Thus, an aspect ratio of the vertical pillar is increased to cause difficulty in a process and diode leaning.
Even in a transistor switching element of a vertical pillar, a height of the vertical pillar is to be also increased to ensure an effective channel length. As in the diode switching element, an aspect ratio of the vertical pillar is increased and thus it may increase a process difficulty and cause a leaning phenomenon.